Latching actuators

ABSTRACT

Latching devices which utilize the residual magnetism retained in the relatively soft magnetic materials of the magnetic curcuit for its latching force. The actuators are proportioned so as to have a minimum effective air gap in the actuated position to achieve a high latching force without the use of a permanent magnet in the magnetic circuit. A means is provided for demagnetizing the magnetic circuit to release the actuator from the actuated position. Various configurations are disclosed, including some ideally suited for use with a simple remote switching means.

United States Patent 1191 3,743,898 Sturman July 3, 1973 LATCHINGACTUATORS 3,349,356 10/1967 Shinohara 335/266 x 3,126,501 3/1964 Fl335/254 x [761 invent l l m! 18643 2,375,017 5/1945 M xison 335/230Kirkcolm Lane, NErtIiridge ICaIif. 9 l 3 24 Primary Examiner-GeorgeHarris [22] Filed; M 27, 1972 Attorney-Spensley, Horn and Lubitz RelatedUS. Application Data Latching devices which utilize the residualmagnetism [63] Continuation-impart of er, N 24,232, March 31 retained inthe relatively soft magnetic materials of the 1970, abandoned. magneticcurcuit for its latching force. The actuators are proportioned so as tohave a minimum effective air [52] U.S. Cl 317/154, 335/254, 335/268 gapin the actuated position to achieve a high latching [51] Int. Cl. H01h47/04 force without the use of a permanent magnet in the [58] Field ofSearch 335/230, 253, 254, magnetic circuit. A means is provided fordemagnetiz- 335/256, 266, 268; 317/123, 154 ing the magnetic circuit torelease the actuator from I a the actuated position. Variousconfigurations are dis- [56] References Cited closed, including someideally suited for use with a sim- UNITED STATES PATENTS ple remoteswitching means. 3,202,886 8/1965 Kramer 335/254 X 19 Claims, 15 DrawingFigures f 2 1 4 i ii i 1 I i i E\ SCONDAPYCOAL r 1 3 \7 L .J 5 5 I g f gP/P/MA/Q Y 60/4 5 5 i 2 A 1 5 1 14 J 5 I -21 )4 m '-I2 l6 1 I v25 *16i2. 3 g 2 Z "(I x E 1 a E, 1 1

I 1 P/P/MAPS (0/4 2 ;A r i k 1 1, Siam/049V 06/2 12 1r v T, I i 1 I 52 1j; K

Patented July 3, 1973 4 Sheets-Sheet l 4 4 m w k w w y m W W m V P r m DR A N A M N w M m E H 2 Z W 5 S P l 2 S 6 m r 2 M N 4 @2 mwwwwmw ro s r!I I 5- M I. m V w m 5 M 1 MAGA/ET/Z/A/G ERCE- 0526/7506 Patented July 3,1973 3,743,898

4 Sheets-Sheet 5 ISO LATCHING ACTUATORS CONTINUATION IN PART Thisapplication is a continuation in part of my application for patententitled Latching Actuator, Ser. No. 24,282 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to solenoid actuators of the latching type.

2. Prior Art Presently the great majority of electrical latching devicesare solenoids of the on-of type, where current is required continuouslyin order to keep the armature at the on position. This type of deviceconsumes extremely large amounts of electrical energy whenever the ontime is larger than the time of armature movement. This excessive energymust be dissipated as heat, and as a consequence, conventional solenoidsare relatively large and heavy.

To overcome the basic limitations of solenoids, various latching deviceshave been constructed. However, all such devices require energy storingmembers such as mechanical biasing elements or permanent magnets. Suchenergy storing members, however, have inherent disadvantages which haveprevented general replacement of the conventional solenoid. Thosedevices utilizing mechanical biasing elements must be supplied withenergy prior to the point at which the actuator is ready for operation.This greatly complicates the mechanism and generally necessitates asubstantial increase in the size of the latching device.

Some of the permanent magnet types of latching actuators have proved tobe more efficient, smaller and lighter than conventional solenoids.Thus, in my application for patent entitled Self-Latching SolenoidActuator, Ser. No. 153,939, now US. Pat. No. 3,683,239, simple andefficient solenoids of this type, particularly suited for operationthrough a simple control circuit, are disclosed. However, the cost ofincorporating apermanent magnet into the solenoid structure issignificant, and if the use of a permanent magnet could be eliminatedwhile still maintaining the simplicity of structure and operation, themanufacturing cost of such devices could be further reduced. Similarly,as shall be subsequently discussed more fully, power consumption inoperation may actually be reduced by elimination of permanent magnet.

To more fully highlight the limitations of devices using permanentmagnets, it is to be noted that the saturation flux density of permanentmagnet materials is substantially lower than the saturation density oftypical soft magnetic materials. Furthermore, to efficiently utilizepermanent magnet materials, the magnet proportions must be designed sothat the permanent magnet operates well down on its demagnetizationcurve. By way of example, for Alnico V, the maximum external energy isachieved with an operating flux density of the permanent magnet ofapproximately 8,500 Gauss. Since the saturation flux density of softmagnetic materials which may be used for the other parts ofa solenoidmay range upwards of 20,000 Gauss, and since the solenoid force isproportional to BA, where B is the flux density and A is the effectivearea of the field, maximum solenoid force will be achieved if thesolenoid area is substantially less than the cross sectional area of thepermanent magnet so as to increase B to the higher saturation density.

Also, it should be noted that a permanent magnet requires a highcoercive force to either magnetize or demagnetize the magnet. Thus, foractuation ofa solenoid device having a permanent magnet, the solenoidcoil must create a sufficient MMF to create a high flux density, both inthe air gap in the magnetic circuit, and in the permanent magnet forminga part of the magnetic circuit. Consequently, to achieve the maximumsolenoid force while the air gap in the solenoid is at or near itsmaximum, a substantially higher MMF is required to be generated by thesolenoid coil than in solenoids not having a permanent magnet, therebyincreasing the energy input to the coil and the FR loss therein. Also,once the solenoid is actuated and latched the unlatching of the solenoidcreates no external mechanical work in that the return of the solenoidmoving member to the unactuated position will be accomplished by areturn spring (or other means). However, to demagnetize a permanentmagnet, a significant electrical energy input to the solenoid coil isrequired to generate the demagnetizing MMF, thereby causing theexpenditure of further electrical energy without obtaining any usefulwork out of the solenoid.

Since a permanent magnet used in the solenoid should have across-sectional area substantially larger than the cross-sectional areaof the solenoid air gap, and further, since permanent magnets tend to bebrittle, easily chipped, etc., permanent magnets should not be used asthe pole face of the solenoid, but instead must be buried" in anotherpart of the magnetic circuit. This characteristically requires asubstantial increase in a number of parts making up the magneticcircuit, thereby increasing manufacturing costs, assembly time andtolerance accumulation.

In summary of the above, there is need for a latching actuator of thesolenoid type which utilizes a minimum number of parts, fabricatablethrough mass production methods of inexpensive materials, and readilyassembleable without substantial machining to achieve a reliablelatching actuator with a high latching force, and which may be easilyand efficiently actuated and unlatched in response to an electricalsignal.

BRIEF SUMMARY OF THE INVENTION Latching devices which utilize theresidual magnetism retained in the relatively soft magnetic materials inthe magnetic circuit for the latching force. The actuators areproportioned so as to have a minimum effective air gap in the actuatedposition to achieve a high latching force without the use of permanentmagnets in the magnetic circuit. Means are also disclosed for applyingpower to the actuators so as to assure the maintenance of at least asubstantial magnetizing current until the moving member of the solenoidreaches the actuated position, whereafter the retentivity of the softmagnetic materials achieves a high latching force even after themagnetizing current decreases to zero. Means are also provided fordemagnetizing the magnetic circuit to release the actuator from theactuated position. Various configurations are disclosed including someideally suited for use with a simple remote switching means. One suchconfiguration includes a switch mechanically coupled to the movingmember of the solenoid so as to switch one solenoid coil lead betweenfirst and second actuator terminals. Various means are also disclosedfor maintaining the required magnetizing current during switching of theswitch coupled to the moving member so that a momentary open of theswitch does not result in the collapse of the magnet field in themagnetic material before the moving member reaches the actuatedposition. The latching devices of the present invention may befabricated from substantially any magnetic material, particularlyrelatively soft magnetic materials selected substantially entirely basedupon the .cost of fabrication thereof, and fabricated in simpleconfigurations which may be assembled with a minimum of individual partsto achieve a latching actuator with a very high latching force.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of atypical latching actuator of the present invention.

FIG. 2 is the hysteresis loop for Ingot Iron.

FIGS. 3a through 3d are schematic representations of the magneticcomponents of the actuator of FIG. 1 illustrating the intensity of themagnetic fields therein under various actuation conditions.

FIG. 4 is a schematic diagram of a typical means for applying electricalpower to the actuator of FIG. 1.

FIG. 5 is a cross-section of an alternate embodiment latching actuatorof the present invention.

FIG. 6 is a schematic illustration of the interconnection and means ofapplying electrical power to the actuator of FIG. 5.

FIGS. 7a through 7c are schematic diagrams of the instantaneous circuitfor the circuit of FIG. 6 at various stages of operation of theactuator.

FIG. 8 is a cross-sectional view of a further alternate embodiment ofthe present invention.

FIG. 9 is a diagram illustrating the interconnection of and the means ofapplying power to the solenoid actuator of FIG. 8.

FIG. 10 is a schematic diagram for an alternate means of applyingelectrical power to the solenoid actuator of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now in detail to FIG. 1,the latching actuator device of one embodiment is comprised of ahousing, generally designated 10, which is constructed of a magneticmaterial. The housing has outer walls 12, and inner walls 14, joined bywall 16. Housing 10 is bordered on opposite ends by pole faces 18 and20. Above wall 16, and between walls 14 and 12, is positioned a firstprimary coil 21. Below wall 16 and between walls 14 and 12 is positioneda second primary coil 22. A first secondary coil 24 is positioned withinthe housing between inner walls 14 and 12 and above primary coil 21 andbelow first pole face 18. A second secondary coil 26 is positionedwithin said housing between inner wall 14 andouter wall 16, below secondprimary coil 22 and above pole face 20.

An armature 28 is slidably mounted within housing 10 and between innerwalls 14. It is free to move linearly within walls 14 and between polefaces 18 and 20. The armature is constructed so that there is virtuallyno air gap between the side of the armature and inner walls 14.Extending vertically from armature 28 is a plunger 30. Pole face 20 hasa hole 32 therein to allow plunger 30 to extend therethrough. Plunger 30then moves with armature 28, as the armature moves up and down withinhousing l0.

Armature 28 may also have a hole 34 therein to correspond with a hole 36within pole face 18. Such an embodiment, would allow for a member (notshown) to extend into armature 28 and be acted upon by the armature inits linear movement.

In operation, when a current is run through primary coil 21, a magneticcircuit is energized creating magnetic flux paths which pull armature 28to pole face 18. When the coil current is turned off, a portion of themagnetic energy will be retained by the magnetic circuit in the form ofresidual magnetism. The invention provides for essentially no air gap inthe latched position and consequently the full residual induction of thematerial can be utilized. As an example, the hysteresis loop for AlnicoMagnetic Ingot Iron is shown in FIG. 2. When the current is turned off,and the magnetizing force is at zero the residual induction has a valueof 10 kilo-gauss. Since the latching force is proportional to the squareof the induction, it is consequently quite high. Therefore, once acurrent is passed through the primary coil, a very strong latching forcecan be maintained long after the current is turned off.

To move the armature in the opposite direction, primary coil 22 isenergized simultaneously with secondary coil 24. Energizing secondarycoil 24, creates a temporary magnetic field which cancels the retainedmagnetic fields set up by primary coil 21, thus eliminating thisresidual magnetism effect leaving the armature free to move. Energizingprimary coil 22 then creates a magnetic field which causes armature 28to move downward and against pole face 20. The residual magnetism effectworks as before, holding armature 28 against pole face 20.

Thus, in operation, the latch actuating device is able to maintain ahigh latching force without the need for mechanical energy storingdevices, such as springs or permanent magnets.

By way of further illustration of the operation of the latching actuatorof FIG. 1, reference is now made to FIGS. 3a through 3d. These figuresare schematic representations of the magnetic components of the solenoid(and further including the nonmagnetic plunger 30) and are for thepurpose of illustrating the primary disposition and intensity of themagnetic fields within the solenoid throughout different phases ofoperation thereof. FIG. 3a shows the solenoid armature 28 latched in theupper position as a result of the relatively high magnetic field,generally indicated by the heavy lines 40. It will be noted that the airgap between the top surface of armature 28 and the lower surface of thefirst pole face 18 is substantially zero. Furthermore, the area of innerwall 14 is very much larger than the area of contact between the firstpole face 18 and the top of armature 28, and further, the gap betweenthe armature and the inner walls is chosen by design to be as small aspossible and still provide for free motion of the armature. Thus,because of'the large area, the radial flux density between the armature28 and inner walls 14 is relatively low, and this together with thesmall air gap therebetween results in only a small demagnetizing forcefor the otherwise magnetized material of the solenoid. Because of thefinite air gap between the armatureand the inner walls (as well as aless than perfect surface contact between the armature 28 and the firstpole face 18) the actual operating point of the magnetic material willbe determined by the intersection of line 42 with the demagnetizationcurve 44 for the particular magnetic material used. The slope of line 42is a measure of the air gaps (and other nonmagnetic ma' terials) in themagnetic circuit, weighted by the effective crosssectional areas of theparticular air gaps. For a circuit having no air gaps line 42 would bevertical, and the flux density in the material would be the flux densityat point 46. On the other hand, if the air gaps in the circuit werelarge and/or the cross-sectional area of the air gap was small, line 42would have a very low slope, such as that of line 48. In this case, theflux density would be that of point 50, a negligible flux density forpurposes of latching (B is very low at point 50). However, by keepingthe air gaps as small as possible, and further by keeping thecross-sectional area of all air gaps as large as possible (with theexception of the air gap across which the primary solenoid force is tobe developed) the slope of line 42 may be kept large so as to result ina relatively large field intensity in the magnetic material, indicatedby point 52. Thus, even soft magnetic materials will retain asubstantial flux density after having been magnetized if the air gapsare kept very small.

To actuate the solenoid from the position shown if FIG. 3a, a current isapplied to primary coil 22 and secondary coil 24 (FIG. 1), preferably byconnecting these two coils in series and passing a current through theseries combination. The number of turns on each secondary coil isselected in proportion to the primary coil so that the secondary coilwill demagnetize the previously magnetized material while the primarycoil will magnetize the surrounding magnetic material and further willcreate a high flux density in the air gap so as to encourage thearmature to the opposite position. By way of example, coil 22 and thecurrent applied thereto are selected so as to create a very high field,indicated by the lines 54 in FIG. 3b, preferably nearly saturating themagnetic material. At the same time, secondary coil 24 ideally shouldcreate a demagnetizing force on the associated magnetic material ofapproximately 1 Oersted (see FIG. 2). This will substantiallydemagnetize the associated magnetic material, as shown by the lightfield lines 40 in FIG. 3b. While perfect demagnetization is in generalnot possible, at least on a repeatable basis, the flux density in theupper portion of the solenoid may be so reduced by this demagnetizingforce as to cause negligible upward force on the armature 28. (In thisregard, it is to be noted that if the flux density in the upper portionof the solenoid is reduced to 20 percent of its value at point 52 (FIG.2), the force urging the armature to the upper position will be only 4percent of the value experienced when the fields are the condition shownin FIG. 3a). Thus, the high magnetic field in the lower portion of thesolenoid, indicated by lines 54, cause a high force between armature 28and the lower pole face 20 so as to urge the armature to the lowerposition. Consequently, the force on the armature will reverse, as shownin FIG. 3b, and the armature will accelerate toward the lower position.When the armature reaches the lower position, as shown in FIG. 30, andcurrent is terminated, the lower portion of the solenoid will remainmagnetized in the same manner as heretofore described with respect tothe upper portion of the solenoid as described in relation to FIG. 3a.At this time, the upper portion of the solenoid will have substantiallyzero flux therein since it was substantially demagnetized as shown inFIG. 3b before the armature moved to the lower position, and furtherbecause the large air gap between the armature 28 and the upper poleface 18 causes a very high demagnetizing force on the magneticmaterials.

To return the armature to the upper position, a magnetizing current isapplied to the primary coil 21 and a demagnetizing current to secondarycoil 26. Thus, the upper portion of the solenoid is strongly magnetizedas shown by the heavy field lines 40 in FIG. 3d, and the lower portionof the solenoid is substantially demagnetized as indicated by the lightfield lines 34. Thus, the armature will accelerate toward the upperposition and will be latched in the upper position upon termination ofthe current, as originally shown with respect to FIG. 3a. It should benoted that when the solenoid is unlatched in one position and forced tothe opposite position, the solenoid current inducing such action mustnot be terminated before the armature arrives at its final position. Ifthe current is terminated before the armature reaches its finalposition, the magnetizing force on the associated portion of thesolenoid magnetic material will fall to zero while there is asubstantial air gap, and thus a very large demagnetizing influence onthe solenoid, so that there will be no substantial residual magneticfield in the solenoid to latch the solenoid at either position, Thus,removal of the solenoid actuating current before the armature reaches asteady state posi tion, will result in the solenoid being substantiallyunlatched in either position.

A suitable circuit for applying power to the solenoid of FIG. 1 is shownin FIG. 4. In this circuit, a spring biased switch, generally indicatedby the numeral 60, is connected to a source of DC power 62. The movingelement of the switch 64 is spring biased to a central off position.(schematically represented by springs 66). When the moving element 64 ismoved to the upper position, power supply 62 is connected through switch60 and line 68 to primary coil 21 and secondary coil 26 to unlatch thearmature, force it to the upper position and latch it at the newposition. When finger pressure is removed from the switch, power isdisconnected from the solenoid, though the solenoid will remain in theupper position because of the latching action thereof. When the movingmember 64 of switch 60 is moved to the lower position, power is appliedthrough coils 22 and 24 to unlatch the solenoid, move it to the lowerposition and latch it at that position. Thus, the switch provides aconvenient means for actuating the solenoid between the upper and lowerpositions, and because the solenoid response is much faster than themanual switching of switch 60, maintenance of actuating current for atleast as long as it takes the armature to reach a new position isassured.

Now referring to FIG. 5, an alternate embodiment of the presentinvention may be seen. This embodiment is substantially the same as thefirst embodiment shown and described in my copending applicationentitled Self-Latching Solenoid Actuator, Ser. No. 153,939, with theexception that the permanent magnet has been removed and the proportionsof the device changed slightly in accordance with the present invention.Thus, an outer nonmagnetic enclosure 70 provides the housing withinwhich the various parts of the solenoid may be assembled and which maybe adapted as desired for mounting of the solenoid. A plunger 72 isdisposed adjacent one end of the case, with an integral plunger rod 74projecting through an opening in the end of the case for attachment tothe mechanism to be actuated by the solenoid. A magnetic inner casemember 76 has an inner diameter 78 forming a loose slip fit with theouter diameter of plunger 72, and has an integral upward projectingcylindrical member 80 forming a portion of the magnetic circuit andproviding an inner diameter for location of the solenoid coil 82. Thus,fitting in the upward projecting member 80 is a solenoid coil 82 woundon a plastic bobbin 84. Also integral with magnetic member 76 is aninner upward projecting cylindrical member 86 projecting upward butterminating substantially short of upper pole piece 88, which completesthe magnetic circuit and retains the various components of the solenoidin cooperative disposition. Thus, the magnetic members of the solenoidcomprise the upper pole piece 88, the plunger 72, and the inner framemember 76, all of which are of simple physical configuration so as to bereadily fabricatable by mass production methods.

Located above the upper pole piece 88 is a nonmagnetic spacer 90, andlocated thereabove at the top of the outer case member 70 is a singlepole, double throw switch 92 having a centrally disposed actuatingmember 94. The switch 92, of the type referred to as micro switches, isretained in position by cementing the switch in place in the case member30 (as are the other parts of the solenoid).

The plunger 72 has a cylindrical depression 96 extending downward fromthe top face 98 of the plunger, and is adapted to receive the switchactuating pin 100. Switch actuating pin 100, which is a nonmagnetic pin,has an enlarged head 102 at the lower end thereof, fitting withincylindrical depression 96 in the plunger 72, and extends upward throughclearance holes in pole piece 88 and the spacer 90 to a positionadjacent switch actuating member 94. A coil spring 104 disposed betweenpole piece 88 and the enlarged head 102 on the switch actuating pin 100,urges the switch actuating pin and plunger 72 to the downward positionshown in FIG. 5.

Now referring to both FIGS. and 6, the electrical connection of thesolenoid may be seen. One lead of the coil 82 is connected to the movingmember 104 of the switch 92 through line 106. The other lead 108 of thesolenoid coil is connected to a remote switching means, generallyindicated by the numeral 110, which may be schematically representableas a single pole double throw switch having a moving member 112. Thisswitch may be a mechanical or electronic single pole double throwswitching means, and may further be biased (mechanically orelectrically) to a central off position, since, as it shall besubsequently more fully described, the switch need only provide amomentary switching signal at either of the two positions. Oneconnection of the switch 110 is coupled through a current limitingmeans, specifically resistor 114, to the negative side of DC powersupply 116. The other contact of switch 110 is coupled to the positiveside of the DC power supply 116. Similarly, one contact of the switch 92is coupled through line 118 to the negative side of the power supply andthe other contact is coupled through line 120 to the positive side ofthe power supply.

Initially both switch contacts 104 and 112 may be in the upper position,as shown in FIG. 6. In this position, both ends of the solenoid coil 82are connected to the negative power supply terminal so that no power isapplied to the solenoid coil. When the moving member 112 of remoteswitch 110 is moved to the lower position, line 108 of the solenoid coil82 is connected to the positive power supply terminal while line 122remains coupled to the negative power supply terminal through line 1 18.Thus, power of a first polarity is applied to the solenoid coil 82causing the solenoid to move toward the actuated position. To latch atthe actuated position it is necessary for the current in solenoid coil82 to persist until the plunger 72 reaches the upper position (FIG. 5)and come to rest against the pole face 88. Consequently, some means mustbe provided to maintain a current in coil 82 until the plunger reachesthe actuated position. One means of achieving the desired result is toprovide a time delay between the motion of plunger 72 and switching ofthe switch 92. Switches of this type have a certain time delay which maybe further enchanced by separating the actuating pin 100 from plunger 72by a coil spring between these two members (not shown). However, it hasbeen found that a time delay in the switching action of switch 92 forcommercially available switches is generally inadequate to assure properlatching of the solenoid, and additional mechanical means for increasingthe time delay as a result of indirect coupling between actuating pin100 and plunger 72 unnecessarily complicates the structure.Consequently, it is generally preferred to provide some other means formaintaining the current.

One such means is provided by diode 124 which is coupled between themoving member 104 of switch 92 and the stationary contact of the switchconnected to line 120. When moving member 104 is in the upper position,diode 124 is back biased and therefore nonconductive. When the movingmember 112 of remote switch 110 is moved to the lower position, the fullvoltage of power supply 116 is applied across solenoid coil 82, therebyresulting in a very high flux in the magnetic circuit of the solenoidcausing the rapid acceleration of solenoid plunger 72 toward theactuated position. Upon initial application of power to the solenoidcoil 82, the electrical connection of a solenoid coil is effectively asshown in FIG. 7a. As the plunger moves toward the actuated position,switch 92 is actuated with moving member 104 going through an opencondition before ultimately making contact with the fixed contactcoupled to line 120. During the time of the open condition, the circuitis as shown in FIG. 7b. Of course, before the moving member 104 moves tothe open position, a relatively high current was caused to flow throughsolenoid coil 82, thereby causing a high magnetic field in the magneticstructure of the solenoid,

preferably approaching the saturation flux density of the magneticmembers of the solenoid. When the moving member 104 moves to the openposition, the magnetic field in the solenoid iron begins to collapse andcreates a back EMF, that is, a voltage of reverse polarity compared tothat of FIG. 7a,-determined by the equation E Nd/dt, where N is thenumber of turns in the solenoid coil and d/dt is the rate of collapse ofthe magnetic field in the solenoid iron. The back EMF, while beingphysically most readily appreciated as a measure of field collapse givenby the above equation, it may be expressed in a different form by notingthat qb LI/N where L is the inductance of the solenoid coil and I is thecurrent therethrough. Thus, Ndldt LdI/dt IdL/dt and the entire loopequation for the instantaneous circuit of FIG. 7 becomes L dI/dt I dL/dtVd [R where R is the resistance in the circuit primarily in the coil 82,and Vd is the diode voltage drop of diode 124. It is to be noted thatthe value of L is constantly changing (increasing) as the plunger movestoward the stationary portion of the solenoid, and further, because ofthe acceleration, the velocity of the plunger is not uniform andtherefore dL/dt is also changing. However, at any point along thetrajectory of the plunger, approximate values for L and dL/dt may besubstituted into the above equation to determine the approximateequation form for the current in the coil at that time. Thus,rearranging the above equation there results The instantaneous solutionof the above equation, making the assumptions as herebefore stated, isan exponential decay of the current from an initial value to a value ofI=Vd/R (this of course is a gross approximation achieved by assuming aconstant value for the time varying perameters within the parenthesisbut is sufficient to illustrate the operation of the circuit. Also, thecurrent could never go negative because of the diode 124, and thereforethe equation and the approximate solution thereof are only applicablefor positive currents). The above equation and the highly approximatesolution thereof are presented merely to illustrate the fact that thecurrent in the solenoid coil and the field in the solenoid iron do notimmediately decrease to zero, but instead merely start to decay at arate determined by the various components of the system.

The micro switches of the type commercially available for use as switch92 are generally designed to rapidly switch between the two alternateswitching positions, and therefore the moving member 104 will veryrapidly make contact with the fixed contact coupled to line 120. Thismotion will be further enhanced, in general, by motion of the actuatingmember 94 as a result of rapid motion of the plunger by the time theactuating member is depressed thereby. Thus, when the switch completesthe switching motion, the circuit will be as shown in FIG. 7c. Thisfigure is substantially the same as that of FIG. 7b, though the diode124 is shorted out and therefore removed from the circuit as a result ofthe switch closure. Thus, the equation for the rate of decay of currentfor this circuit is given as follows:

which in general is similar to the above equation but with a somewhatlower rate of decay of current, and therefore field strength, in thesolenoid. When the plunger arrives at the actuated position, theinductance is at a maximum and is constant thereafter so that theequation defining the conditions of the circuit of FIG. 7c furthersimplifies to the following:

dI/dt IR/L O The solution of this last equation, of course, is a trueexponential decay in current to zero.

The purpose of the above equations is merely to illustrate the manner inwhich the diode allows the maintance of a substantial magnetizingcurrent to remain in the solenoid coil, even when switch 92 is movingthrough the open condition, so as to prevent the collapse of themagnetic field in the solenoid before the solenoid plunger reaches theactuated position. Once in the actuated position the further decay ofthe magnetizing current to zero is of little consequence, inasmuch asthe residual flux in the solenoid iron maintains a high latching forceeven after the current decays essentially to zero. Thus, it may be seenthat the diode prevents an open circuit as switch 92 switches from afirst position to a second position so as to maintain a substantialmagnetizing current in the solenoid coil, at least until the plungerarrives at the latched position. Furthermore, it should be noted that inmost applications, a solenoid is actuating a load which is substantiallyinertial, and though actuation of the solenoid generally requires atleast a few milliseconds, most of the actuation time is used inestablishing the magnetic field in the solenoid and in initiallyaccelerating the plunger toward the actuated position. Thus, by the timeswitch 92 first starts switching and moves into the open position, theplunger is rapidly moving toward the latched position so that themagnetizing current need only be maintained as hereabove described for avery short time. Thus, the flux in the solenoid will decrease onlyslightly in order to create the back EMF to maintain the magnetizingcurrent until latching is achieved.

To maintain the latching force, even in the presence of this slightdecrease in flux, the contacting pole faces may be chamfered so as toconcentrate the flux and therefore increase the flux density over thepole face to achieve higher latching forces. (Since the solenoid forceis proportional to B A or dfi/A, where is the total flux and A is thearea over which the flux is distributed, the latching force for a givenflux may be increased by decreasing the area over which theflux isdistributed). Thus, chamfers 150 and 152 are provided in the solenoid ofFIG. 5. It should be further noted, referring again to FIG. 2, that theresidual flux density in the exemplary material is approximately 10,000Gauss. The saturation flux density for the same material isapproximately 15,000 Gauss, and is approached with a magnetizing forceof only approximately 8 Oersteds. Thus, the latching force may befurther increased by further decreasing the contact area of the plungerwith the pole 88, thereby further concentrating the flux to approach thesaturation flux density for the material at that point. This may beachived with only a very slight drop in total fiux in the solenoid,since the concentration of flux is very local in nature and thus the HLdrop (coercive force in Oersted inches) due to the concentration is verylow because of the very short effective length L in the region ofconcentration, and may easily be made up by the remaining 95 percent ofthe magnetic circuit as a result of a slightly higher demagnetizingforce thereon. By way of specific example, 95 percent of the iron in themagnetic circuit may be operated at a flux density, at point 150, ofapproximately 7,000 Gauss instead of approximately 8,500 Gauss at point52. Since the demagnetizing force of point is approximately one fourthof an oersted greater than at point 52 and represents the demagnetizingforce of approximately 95 percent of the circuit, the additionaldemagnetizing force in this part of the circuit results in a magnetizingforce per unit length of approximately 20 times one fourth orapproximately 5 oersteds in the area of flux concentration. Thus, it maybe seen in FIG. 2 that the flux density for latching may beapproximately 14,000 Gauss achieved as a result of proportioning themagnetic circuit and chamfering the plunger pole face so as to reducethe plunger contact area in the latched condition to approximately onehalf that of the average cross sectional area of the solenoid iron.Further, if the chamfering (or other method of reducing the pole facearea of contact such as by putting a groove pattern on the pole face,etc.) is slight, the gap in the chamfered area may be relatively largewhen the solenoid is in the latched position but may be small incomparison with the air gap when the solenoid is in the unactuated oronly partially actuated position. Thus, the effective pole face area ofthe unactuated position may be approximately twice that of the actuatedposition. Consequently, assuming the initial solenoid current to beadequate to substantially saturate the solenoid iron, approximatelytwice the total flux will exist in the solenoid during the initialmotion of the plunger and a high initial force of the solenoid will beachieved. Furthermore, the total flux may decay by a factor ofapproximately 50 percent while maintaining a substantial magnetizingcurrent ashereabove explained with respect to FIGS. 70 through 7d, andresult in a very high latching force as a result of the near saturationof the plunger pole face in the actuated position, even in the absenceof any continuous latching current.

To unlatch the solenoid, the moving member 112 of the remote switch 110is again moved to the upper position. Thus, coil 82 is again coupledacross power supply 116 with an opposite polarity from that heretoforedescribed, and with current limiting means, namely resistor 114, inseries with the circuit. By properly selecting the resistor 114 inconjunction with the voltage of the power supply 116 and thecharacteristics and dimensions of the solenoid members, the currentthrough the solenoid coil 82 may be caused to provide a demagnetizingforce on the solenoid iron to reduce the flux density at the pole faceof the plunger to approximately zero. For the exemplary material of FIG.2, approximately one oersted demagnetizing force is required to achievethis object. This magnetizing force, of course, is very low incomparison to the required magnetizing force for normal permanent magnetmaterials (by way of example the demagnetizing force of Alnico V isapproximately 700 Oersteds). Thus, with the expenditure of only a veryslight amount of electrical power, the solenoid iron is substantiallydemagnetized and the return spring 104 will accelerate the solenoidplunger toward the unactuated position again.

Switch 92, when actuated by the downward motion of the plunger, will gothrough an open position. However, assuming the solenoid iron to befairly soft, a significant air gap will result in such a demagnetizingforce on the solenoid materials so as to prevent a significant force toresult from the recovery of the field upon removal of the demagnetizingcurrent. (If the demagnetizing current is terminated when there are noother demagnetizing influences in the solenoid material e.g. the airgapis still substantially zero, the field will recover from substantiallyzero at point 160, along a line 162 approximately parallel to the slopeof the demagnezation curve at point 46, to point 164, thereby providinga sufficient flux to relatch the solenoid). If the solenoid iron issomewhat magnetically harder than the exemplary material of FIG. 2,there may be a substantial recovery in the flux density in the air gapwhen the switch moves to the open position, the effects of which mayagain be minimized by the use of a second diode 166 to maintain asubstantial demagnetizing current in the solenoid coil until the plungermoves to the fully extended position, in much-the same manner as thatheretofore described with respect to operation of diode 124.

One further embodiment for a latching actuator which latches at bothextremes of its stroke, using the principles of the present invention,is shown in FIG. 8, and a suitable means for applying power to theactuator of FIG. 8 is shown in FIG. 9. The actuator of this embodimentis comprised of an upper magnetic member 200a, a lower magnetic member200 b, both of which may be identical members, a magnetic plunger 202and a nonmagnetic actuating pin 204 for connection to the load to beactuated by the actuator. A first coil 206 is located in member 200a andsecond coil 208 is located in member 200b, coils 206 and 208 beingidentical coils. When a magnetizing current is applied through coil 208,the plunger 202 will be magnetically attracted to the top face of member200b, and because of the flat surfaces of member 202 and of 200a and200b, will lie flat against member 200b, thereby resulting insubstantially zero air gap therebetween. Thus, there will be a very highmagnetic field, indicated by lines 210, through the magnetic componentsdue to the retentivity of the soft magnetic material and the extremelysmall demagnetizing force thereon (e.g. substantially zero). To actuatethe solenoid to the upper position and latch the solenoid plunger 202against the bottom face of member 200a, a high magnetizing current isapplied through coil 206 while at the same time a small demagnetizingcurrent is applied to coil 208. This demagnetizes the lower portion ofthe solenoid while magnetizing the upper portion, causing the plunger202 to move to the upper position and be latched thereat in a mannerheretofore described.

The excitation of the coils of the solenoid of FIG. 8

may be accomplished by any suitable means, such as by way of example themeans shown in FIG. 9. Here the coils 206 and 208 each have one leadthereof connected to a ground terminal. The moving member of a springbiased switch 212 may be used to momentarily couple line 214 to eitherthe positive or the negative side of a balanced power supply 216. Eachof coils 206 and 208 is coupled to line 214 through a parallelconnection of a resistor and a diode. Thus, resistor 218 and diode 220are coupled with coil 206 to line 214, with the diode providingsubstantially direct connection of line 214 to the coil 206 when line214 is positive, and the resistor 218 providing a current limiting means(with the diode back biased) when line 214 is negative. Similarly,resistor 222 and diode 224 couple coil 208 to line 214, substantiallydirectly when line 214 is negative, and through the current limitingresistor 222 when line 214 is positive. Thus, when switch 212 couplesline 214 to the positive terminal, the high magnetizing current iscaused to flow in coil 206, whereas a small, predetermined,demagnetizing current is caused to flow in coil 208. Thus, the lowerportion of the solenoid will be demagnetized and the upper portionmagnetized so as to force the plunger 202 to the upper position andlatch it at that position. When line 214 is connected to the negativeterminal, a demagnetizing current is caused to occur in coil 206 and astrong magnetizing current is caused to occur in coil 207, therebydemagnetizing the upper portion of the solenoid and strongly magnetizingthe lower portion, thereby actuating and latching the solenoid.

The solenoid of FIG. 8 utilizes only three magnetic members,specifically plunger 202 and members 200a and 200b, two of which areidentical. In the embodiment shown, the various members of the solenoidmay be assembled with a non-magnetic spacer 230, which may be analuminum or a plastic ring. This assembly may be placed in the housingin which it is to be used, or as an intermediate assembly may beretained in the assembled position by suitable means such as anonmagnetic outer case member 232, which may be an aluminum tubularmember rolled or otherwise crimped at the ends thereof to retain theassembly. Of course, as an alternate, one of the members 200a and 200band in the coil therein might be replaced with a nonmagnetic member, anda return spring coupled between the plunger and the remaining members soas to return the plunger to an unlatched condition when the magneticmembers are demagnetized. Such a return spring is typically selected toprovide a return force of approximately one half of the gross solenoidforce so that the net solenoid forces during actuation and whenunlatched are approximately one half of the magnetic force generated.

The latching actuators previously described herein all achieve a highlatching force without requiring any continuous power applied thereto.Such actuators are ideally suited for battery operation as powerdissipation therein is held to a minimum to result in the maximumbattery life. In such applications, the source of excitation such as, byway of example, the power source 116 of FIG. 6 might be comprised of abattery adapted to charge a capacitor through a current limitingresistor so that the charge on the capacitor (or more typically a smallpercentage of such charge) may be used to actuate or unlatch theactuator without requiring a high current from the battery. In otherapplications however, it may be desired to actuate and latch theactuator on a single electrical input, and then unlatch upon the removalof that input. Thus, by way of example, solenoid actuators are commonlyused in both AC and DC devices to actuate and remain actuated upon theapplication of power thereto, and to unlatch upon removal of the power.Thus, by way of example, in appliances such as washing machines, asolenoid valve will be used for control of the water input. Suchsolenoids are generally adapted to operate from an AC power source andgenerally are connected so as to receive the entire line voltage notonly during actuation, but throughout the time period in which thesolenoid is maintained in the actuated position. Thus, by far thegreatest energy is dissipated in the solenoid not during actuation, butrather during the prolonged time period thereafter in which the solenoidis retained in the actuated position. The problem is even somewhat worsein the case of DC actuation, since at least in AC actuation theincreased inductance of the solenoid .when in the actuated positiontends to reduce the current input thereto, though in both AC and DCsolenoids which are to actuate and remain in the actuated position byfull application of power thereto, the size of the solenoid isdetermined more by the heat dissipation after actuation than duringactuation. I

For such applications, the actuator of FIG. may be used with only minormodification thereto so as to achieve the latching actuator which, whenconnected to a power supply will actuate with a relative highmagnetizing current therein, and will automatically switch so as to drawa greatly reduced current to remain in the latched condition. Sinceactuation requires only a fraction of a second to achieve (typically asin the order of milliseconds) the amount of energy dissipated at thehigher current is small, and the small retaining current results inlittle power dissipation in the solenoid. Thus solenoids substantiallysmaller than heretofore used in dishwashers and the like may be used,thereby resulting in smaller and less expensive solenoid devices forsuch applications. This may be achieved by using the solenoid which isbasically the device of FIG. 5 connected to a source'of power as shownin FIG. 10. Thus, in this figure, the source of power 304, which may bean AC or a DC power source, is generally controlled through a switch302, which may be a mechanical or an electronic switch, andcharacteristically for appliances of the type heretofore mentioned is amechanical switch operated by a mechanical timer mechanism. Thesolenoid, generally located within the indicated enclosure, has asolenoid coil 82 connected to switch 302 and also connected to a switch92a. The switch 92a is generally similar in arrangement and function asthe switch 92 in FIG. 5, with the exception that only a single pole,single throw switch is required. Thus, when switch 92a is in theposition shown, one end of the solenoid coil is coupled through theswitch to the power supply. A resistor 300 is also coupled between thepower supply lead and the solenoid coil lead, so that when switch 92a isswitched to the open position, the solenoid coil is cou pled through theresistor 300 to the power supply.

The result of this circuit is as follows. When switch 302 is open, thesolenoid is generally in the unlatched position. When switch 302 isclosed, the full voltage of the power supply 304, whether AC or DC, isapplied across coil 82, thus causing a high MMF in the solenoid to causethe actuation thereof. As the moving member 72 of the solenoid movestoward the actuated position, and preferably as it approaches theactuated position, (or even after it reaches the actuated position, ifsufficient time lag or hysteresis is built into the switching mechanism)switch 92a moves to the open position. Thus the current in coil 82decreases from the high initial actuating current to a substantiallyreduced current, determined by the resistor 300 and the other circuitparameters. However, since actuation of the switch only occurs as themoving member 72 approaches the actuated position, the magnetizingcurrent required to continue the operation of the solenoid and to latchthe moving member in the actuated position is greatly reduced, and thusby proper selection of the value of resistor 300, the magnetizingcurrent may be reduced as a result of the switching of switch 92a to avalue which is still adequate to latch the solenoid.

By way of specific example, assume that the solenoid is intended tooperate from a DC power supply, and generally operates an inertial load.The switch 92a may be adjusted to switch to the open position, at leaststatically, when the moving member has traveled percent of the stroketoward the actuated position. Thus, neglecting any time lag ormechanical hysteresis in switch 92a, and further neglecting the factthat the high initial magnetizing current will not immediately decay toa value determined by resistor 300, but will only change to the lowervalue with some characteristic time constant, resistor 300 may be chosenso as to reduce the magnetizing current in the solenoid coil toapproximately 20 percent of the initial value and still substantiallysaturate the solenoid iron. Thus, the total power dissipated has beenreduced by a factor of five, and further, the power actually dissipatedin coil 82 to achieve latching, that is the PR loss in the coil, is onlyapproximately for percent of the PR loss during initial actuation.

When switch 302 is opened, the magnetizing current drops to zero. Thiscauses a substantial decrease in the field strength in the solenoid, andby proper selection of the return spring (or other return means) thesolenoid may be caused to unlatch and return to the unactuated positionwhen magnetizing current is removed. (To assure a sufficient drop in thefield strength of the solenoid to unlatch the solenoid, it may bedesirable to plate with a nonmagnetic material, by way of example, themoving member surfaces so as to result in a controlled minimum air gapin the solenoid to assure a sufficient effective demagnetizing forcewhen in the actuated position to cause a substantial drop in the fieldupon complete termination of the magnetizing current. In this regardhowever, it should be noted that a drop in field strength of only 50percent, say from substantial saturation to point 150 in FIG. 2, willcause a drop in solenoid force of 75 percent, allowing selection of thereturn means to provide the desired return force).

There has been described in detail herein a number of embodiments of thepresent invention Latching Actuator, as well as a number of alternatemeans for properly applying electrical power to the actuator so as toachieve the desired results of the present invention. In part, thepresent invention comprises solenoids designed to have a minimumeffective air gap when in the actuated position, either or both byminimizing the length of the air gap or gaps and by maximizing theeffective cross sectional area of the air gaps. The solenoids may beassembled from a minimum member of parts of simple geometry and of anymagnetic material, typically relatively soft magnetic material, whichmay be selected primarily for ease of fabrication directly to thedesired configuration with a minimum or absence of machining after basicforming. By way of example, the magnetic components may be formed bywell known powder metallurgy methods so as to result in magnetic partsof finished dimension which will provide the high latching force in thelatched condition. Of course, machined parts may also be used,fabricated by way of example from low carbon steel, such as, C1010 andC1020, etc., either hot rolled or cold rolled, and used directly asobtained from an automatic turning machine,

The term soft magnetic material" and equivalent terms as used hereinhave no specific quantitative definition, but is used herein todistinguish from materials commonly used for permanent magnets becauseof their high retentivity While solenoids having very high latchingforces may be fabricated from even the softest materials such asannealed hydrogenizedirons, such irons are expensive and difficult tofabricate,an'd thus in general, somewhat harder materials are mostpractical because of overall cost considerations, though in generalmaterials having a coercive force of less than Oersteds are probably themost practical materials. Also, it should be noted that the effectiveair gap that may be used in a solenoid of the present invention andstill achieve the high latching forces will depend on the coercive forceof the material used. For annealed hydrogenized irons, the tolerable airgap is very small, and configurations such as that of FIG. 8 are best,while slightly harder materials will provide higher latching forces forconfigurations having some gap in the actuated position, such as that ofFIGS. 1 and 5, (a high radial force will cause the plunger to lieagainst one side of the stationary member, thereby effectively reducingthe clearance or air gap-therebetween). Thus the design criteria is thatthe length of any air gaps be held sufficiently small and the area ofany air gaps (the word air including all nonmagnetic gaps in themagnetic circuit) be maintained sufficiently large, (except for theprimary solenoid pole faces on which the solenoid force is created) sothat the total demagnetization force (Oersted inches) of such gaps isonly a fraction of the coercive force (Oersted inches) of the materialsused even with relatively high flux densities (preferably at leastpercent of the residual density of point 46, FIG. 2) in the magneticcircuit when the plunger is in the latched position.

Also included as part of the present invention are the various means forapplying electrical power to the actuator to assure proper latching witha high latching force. Thus, the actuator of the present invention maybe fabricated from a minimum number of parts selected substantiallyentirely-upon the cost of the fabricated part, to result in an extremelylow cost latching actuator having a latching force which may equal orexceed that of an actuator having a permanent magnet therein, and whichmay be easily actuated without complicated actuation circuits. Thus,while the invention has been particularly shown and described withreference to preferred embodiment thereof, it will be understood bythose skilledv in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

I claim:

1. A latching solenoid actuator having a stationary member and a movingmember adapted for motion between first and second orientations withrespect to said stationary member, and a solenoid coil, said stationarymember and said moving member forming a magnetic circuit and both beingfabricated of magnetic materials exhibiting the magnetic characteristicsof generally soft magnetic materials, said solenoid coil being disposedwith respect to said magnetic circuit so as to cause a magnetizing forcein said circuit in response to a current therethrough, said stationarymember and said moving member being adapted to magnetically urge saidmoving member toward said first orientation with respect to saidstationary member in response to the establishment of a magnetic fieldin said magnetic circuit, said stationary member and said moving memberhaving cooperatively disposed surfaces so as to result in a minimum airgap in said circuit when in said first orientation, whereby theretentivity of said magnetic materials causes a high latching force insaid first orientation whenever said moving member reaches said firstorientation before the current in said coil causing said magnetizingforce is terminated.

2. The latching actuator of claim 1 for linear actuation wherein saidmoving member has a generally flat first surface perpendicular to thedirection of motion of said moving member and a generally cylindricalsecond surface parallel to said direction of motion, said stationarymember having a first surface parallel to said first surface of saidmoving member and a second surface adjacent to and providing a clearancewith respect to said second surface of said plunger, said first sur-'faces being in substantial contact when said moving member is in saidfirst orientation.

3. The latching actuator of claim 2 wherein said second surfaces haveareas which are much larger than said first areas.

4. The latching actuator of claim 1 for linear actuation wherein saidmoving member and said stationary member each have first and secondareas substantially perpendicular to the direction of motion of saidmoving member, said magnetizing force causing a magnetic field to occurin the air gap between said first surfaces and in the air gap betweensaid second surfaces, said first surfaces and said second surfaces beingdisposed so as to be in substantial contact when said actuator is in thelatched position.

5. The latching actuator of claim 4 wherein the area of at least onepair of said first and second areas is substantially less than thecross-sectional area of said magnetic circuit in regions remote to saidfirst and second areas.

6. The latching actuator of claim 1 further comprised of a means forselectively causing a momentary magnetizing current to flow in said coilfor a time period at least as long as the time required for said movingmember to move to said first orientation and a demagnetizing means forcausing the substantial demagnetization of said magnetic circuit.

7. The latching actuator of claim 6 wherein said demagnetizing means iscomprised of a second coil disposed with respect to said magneticcircuit so as to cause a demagnetizing force in said circuit in responseto a current therethrough, and a means for selectively causing ademangetizing current in said demagnetizing means.

8. The latching actuator of claim 6 wherein said demagnetizing meanscomprises a means for selectively causing a predetermined current insaid solenoid coil which is substantially less than and of oppositepolarity from said magnetizing current.

9. A solenoid actuator having a stationary member and a moving memberadapted for motion between first and second orientations with respect tosaid stationary member, a solenoid coil having first and second leads, aswitch and a current maintaining means, said stationary member and saidmoving member forming a magnetic circuit and both being fabricated ofmagnetic materials exhibiting the magnetic characteristics of generallysoft magnetic materials, said solenoid coil being disposed with respectto said magnetic circuit so as to cause a magnetizing force in saidcircuit in response to a current therethrough, said stationary memberand said moving member having cooperatively disposed surfaces so as toresult in a minimum air gap when in said first orientation, and furtherbeing adapted to magnetically urge said moving member toward said firstorientation with respect to said stationary member in response to theestablishment ofa magnetic field in said magnetic circuit,said switchbeing electrically coupled to said first solenoid coil lead and adaptedto switch electrical coupling with said first solenoid coil lead betweenfirst and second actuator leads in response to motion between saidstationary member and said moving member, said current maintaining meansbeing a means for maintaining a substantial magnetizing current in saidsolenoid coil during the time of actuation of said moving member fromsaid second orientation to said first orientation.

10. The solenoid actuator of claim 9 wherein said current maintainingmeans comprises said switch and its mechanical coupling to saidstationary and said moving members, whereby switching of said switch isdelayed during the motion of said moving member from said secondorientation to said first orientation until said moving member comes torest at said first orientation.

11. The solenoid actuator of claim 9 wherein said current maintainingmeans comprises a diode coupled between said first solenoid coil leadand said first actuator lead, whereby a magnetizing current may becaused to flow in said solenoid coil when said moving member is in saidsecond orientation by applying power to said second actuator lead andsaid current may be substantially maintained through said diode duringswitching of said switch by the back EMF of said solenoid coil.

12. The latching actuator of claim 9 for linear actuation wherein saidmoving member has a generally flat first surface perpendicular to thedirection of motion of said moving member and a generally cylindricalsecond surface parallel to said direction of motion, said stationarymember having a first surface parallel to said first surface of saidmoving member and a second surface adjacent to and providing a clearancewith respect to said second surface of said moving member, said firstsurfaces being in substantial contact when said moving member is in saidfirst orientation.

13. The latching actuator of claim 12 wherein said second surfaces haveareas which are much larger than said first areas.

14. The latching actuator of claim 9 for linear actuation wherein saidmoving member and said stationary member each have first and secondareas substantially perpendicular to the direction of motion of saidmoving member, said magnetizing force causing a magnetic field to occurin the air gap between said first surfaces and in the air gap betweensaid second surfaces, said first surfaces and said second surfaces beingdisposed so as to be in substantial contact when said actuator is in thelatched position.

15. The latching actuator of claim 14 wherein the area of at least onepair of said first and second areas is substantially less than thecross-sectional area of said magnetic circuit in regions remote to saidfirst and second areas.

16. The latching actuator of claim 9 further comprised of ademagnetizing means for causing the substantial demagnetization of saidmagnetic circuit.

17. A solenoid actuator having a stationary member and a moving memberadapted for motion between first and second orientations with respect tosaid stationary member, a solenoid coil having first and second leads, aswitch arid a current limiting means, said stationary member and saidmoving member forming a magnetic circuit and both being fabricated ofmagnetic materials exhibiting characteristics of generally soft magneticmaterials, said solenoid coil being disposed with respect to saidmagnetic circuit so as to cause a magnetizing force in said circuit inresponse to a current therethrough, said stationary member and saidmoving member having cooperatively disposed surfaces so as to result ina predetermined air gap when in said first orientation, and furtherbeing adapted to magnetically urge said moving member toward said firstorientation with respect to said stationary member in response to theestablishment of a magnetic field in said magnetic circuit,

said switch and said current limiting means being electrically coupledbetween said first solenoid coil lead and an actuator connection wherebysubstantially direct coupling between said actuator connection and saidfirst solenoid coil lead is achieved when said switch is in a firstposition but said coupling is limited by said current limiting meanswhen said switch is in a second position, said switch being adapted toswitch to said second position as said moving member approaches saidfirst position.

18. The solenoid actuator of claim 17 whereby said current limitingmeans is a resistor and said switch is a single pole single throwswitch, said switch and said resistor being coupled in parallel.

I 19. The actuator of claim 17 further comprised of a return means forreturning said moving member to said second position, said return meanshaving a predetermined return force when said moving member is in saidfirst position which exceeds the force urging said moving member towardsaid first position due to the retentivity of said stationary and saidmoving member, and is less than the force urging said moving membertoward said first position due to the combined effects of saidretentivity and a magnetizing current in said solenoid coil limited bysaid current limiting means.

1. A latching solenoid actuator having a stationary member and a movingmember adapted for motion between first and second orientations withrespect to said stationary member, and a solenoid coil, said stationarymember and said moving member forming a magnetic circuit and both beingfabricated of magnetic materials exhibiting the magnetic characteristicsof generally soft magnetic materials, said solenoid coil being disposedwith respect to said magnetic circuit so as to cause a magnetizing forcein said circuit in response to a current therethrough, said stationarymember and said moving member being adapted to magnetically urge saidmoving member toward said first orientation with respect to saidstationary member in response to the establishment of a magnetic fieldin said magnetic circuit, said stationary member and said moving memberhaving cooperatively disposed surfaces so as to result in a minimum airgap in said circuit when in said first orientation, whereby theretentivity of said magnetic materials causes a high latching force insaid first orientation whenever said moving member reaches said firstorientation before the current in said coil causing said magnetizingforce is terminated.
 2. The latching actuator of claim 1 for linearactuation wherein said moving member has a generally flat first surfaceperpendicular to the direction of motion of said moving member and agenerally cylindrical second surface parallel to said direction ofmotion, said stationary member having a first surface parallel to saidfirst surface of said moving member and a second surface adjacent to andproviding a clearance with respect to said second surface of saidplunger, said first surfaces being in substantial contact when saidmoving member is in said first orientation.
 3. The latching actuator ofclaim 2 wherein said second surfaces have areas which are much largerthan said first areas.
 4. The latching actuator of claim 1 for linearactuation wherein said moving member and said stationary member eachhave first and second areas substantially perpendicular to the directionof motion of said moving member, said magnetizing force causing amagnetic field to occur in the air gap between said first surfaces andin the air gap between said second surfaces, said first surfaces andsaid second surfaces being disposed so as to be in substantial contactwhen said actuator is in the latched position.
 5. The latching actuatorof claim 4 wherein the area of at least one pair of said first andsecond areas is substantially less than the cross-sectional area of saidmagnetic circuit in regions remote to said first and second areas. 6.The latching actuator of claim 1 further comprised of a means forselectively causing a momentary magnetizing current to flow in said coilfor a time period at least as long as the time required for said movingmember to move to said first orientation and a demagnetizing means forcausing the substantial demagnetization of said magnetic circuit.
 7. Thelatching actuator of claim 6 wherein said demagnetizing means iscomprised of a second coil disposed with respect to said magneticcircuit so as to cause a demagnetizing force in said circuit in responseto a current therethrough, and a means for selectively causing ademangetizing current in said demagnetizing means.
 8. The latchingactuator of claim 6 wherein said demagnetizing means comprises a meansfor selectively causing a predetermined current in said solenoid coilwhich is substantially less than and of opposite polarIty from saidmagnetizing current.
 9. A solenoid actuator having a stationary memberand a moving member adapted for motion between first and secondorientations with respect to said stationary member, a solenoid coilhaving first and second leads, a switch and a current maintaining means,said stationary member and said moving member forming a magnetic circuitand both being fabricated of magnetic materials exhibiting the magneticcharacteristics of generally soft magnetic materials, said solenoid coilbeing disposed with respect to said magnetic circuit so as to cause amagnetizing force in said circuit in response to a current therethrough,said stationary member and said moving member having cooperativelydisposed surfaces so as to result in a minimum air gap when in saidfirst orientation, and further being adapted to magnetically urge saidmoving member toward said first orientation with respect to saidstationary member in response to the establishment of a magnetic fieldin said magnetic circuit, said switch being electrically coupled to saidfirst solenoid coil lead and adapted to switch electrical coupling withsaid first solenoid coil lead between first and second actuator leads inresponse to motion between said stationary member and said movingmember, said current maintaining means being a means for maintaining asubstantial magnetizing current in said solenoid coil during the time ofactuation of said moving member from said second orientation to saidfirst orientation.
 10. The solenoid actuator of claim 9 wherein saidcurrent maintaining means comprises said switch and its mechanicalcoupling to said stationary and said moving members, whereby switchingof said switch is delayed during the motion of said moving member fromsaid second orientation to said first orientation until said movingmember comes to rest at said first orientation.
 11. The solenoidactuator of claim 9 wherein said current maintaining means comprises adiode coupled between said first solenoid coil lead and said firstactuator lead, whereby a magnetizing current may be caused to flow insaid solenoid coil when said moving member is in said second orientationby applying power to said second actuator lead and said current may besubstantially maintained through said diode during switching of saidswitch by the back EMF of said solenoid coil.
 12. The latching actuatorof claim 9 for linear actuation wherein said moving member has agenerally flat first surface perpendicular to the direction of motion ofsaid moving member and a generally cylindrical second surface parallelto said direction of motion, said stationary member having a firstsurface parallel to said first surface of said moving member and asecond surface adjacent to and providing a clearance with respect tosaid second surface of said moving member, said first surfaces being insubstantial contact when said moving member is in said firstorientation.
 13. The latching actuator of claim 12 wherein said secondsurfaces have areas which are much larger than said first areas.
 14. Thelatching actuator of claim 9 for linear actuation wherein said movingmember and said stationary member each have first and second areassubstantially perpendicular to the direction of motion of said movingmember, said magnetizing force causing a magnetic field to occur in theair gap between said first surfaces and in the air gap between saidsecond surfaces, said first surfaces and said second surfaces beingdisposed so as to be in substantial contact when said actuator is in thelatched position.
 15. The latching actuator of claim 14 wherein the areaof at least one pair of said first and second areas is substantiallyless than the cross-sectional area of said magnetic circuit in regionsremote to said first and second areas.
 16. The latching actuator ofclaim 9 further comprised of a demagnetizing means for causing thesubstantial demagnetization of said magnetic circuit.
 17. A solenoidactuator having a statioNary member and a moving member adapted formotion between first and second orientations with respect to saidstationary member, a solenoid coil having first and second leads, aswitch and a current limiting means, said stationary member and saidmoving member forming a magnetic circuit and both being fabricated ofmagnetic materials exhibiting characteristics of generally soft magneticmaterials, said solenoid coil being disposed with respect to saidmagnetic circuit so as to cause a magnetizing force in said circuit inresponse to a current therethrough, said stationary member and saidmoving member having cooperatively disposed surfaces so as to result ina predetermined air gap when in said first orientation, and furtherbeing adapted to magnetically urge said moving member toward said firstorientation with respect to said stationary member in response to theestablishment of a magnetic field in said magnetic circuit, said switchand said current limiting means being electrically coupled between saidfirst solenoid coil lead and an actuator connection wherebysubstantially direct coupling between said actuator connection and saidfirst solenoid coil lead is achieved when said switch is in a firstposition but said coupling is limited by said current limiting meanswhen said switch is in a second position, said switch being adapted toswitch to said second position as said moving member approaches saidfirst position.
 18. The solenoid actuator of claim 17 whereby saidcurrent limiting means is a resistor and said switch is a single polesingle throw switch, said switch and said resistor being coupled inparallel.
 19. The actuator of claim 17 further comprised of a returnmeans for returning said moving member to said second position, saidreturn means having a predetermined return force when said moving memberis in said first position which exceeds the force urging said movingmember toward said first position due to the retentivity of saidstationary and said moving member, and is less than the force urgingsaid moving member toward said first position due to the combinedeffects of said retentivity and a magnetizing current in said solenoidcoil limited by said current limiting means.